Hole Saws: Toothed Strip Rolled into a Cup

A hole saw is a steel cup with teeth on its rim, driven by an arbor that carries a pilot drill at the centre. One method starts from flat strip: the teeth are stamped and then ground along one edge, the strip is bent into a tube with the teeth at one end, the seam is welded and its bead ground off, the tube is heat-treated to harden the teeth, and a cap is fitted. Better saws are bi-metal: a carbon steel cup with high-speed steel teeth welded on.